Not a GROUP BY expression error [duplicate]

Answer 1

SELECT MEMBERS.MEMBER_ID,
       MEMBERS.MEMBER_NAME, 
       COUNT(personal_training_sessions.session_id)

FROM MEMBERS JOIN personal_training_sessions
ON personal_training_sessions.member_id=members.member_id

GROUP BY personal_training_sessions.session_id;

You are using a COUNT function, thus the other columns, MEMBER_ID & MEMBER_NAME, must be included in the group by clause.